/* 
    @extend 进行继承
*/
.btn{
    width: 200px;
    height: 50px;
    a{
        color: red;
        &:hover{
            background-color: orange;
            color: yellow
        }
    }
}
.btn-primary{
    @extend .btn;
    background-color: blue;
}

.btn-success{
    @extend .btn;
    background-color: green;
}